Apparatus for producing reduced iron and compact drying

ABSTRACT

An apparatus for producing reduced iron, and a compact drying method for application to the apparatus are disclosed. The apparatus comprises a pelletizer or a briquetter for mixing and agglomerating coal as a reducing agent and iron ore as iron oxide to form compacts, a dryer for drying the compacts, a circular rotary hearth type reducing furnace for reducing the dried compacts in a high temperature atmosphere, a first heat exchanger for performing heat exchange between a hot off-gas discharged from the reducing furnace and combustion air to be supplied to the reducing furnace, and coolers for cooling the hot off-gas. A second heat exchanger for heating drying air is disposed on an exit side of the first heat exchanger. The drying air heated by the second heat exchanger is supplied to the dryer to dry the compacts with the drying air which is scant in moisture. Consequently, highly efficient, stable drying in the dryer can be performed, and high quality reduced iron can be produced stably.

This application is a divisional continuation divisionalcontinuation-in-part of co-pending now U.S. Pat. No. 6,372,016Application Ser. No. 09/610,478, filed on Jul. 5, 2000, the entirecontents of which are hereby incorporated by reference and for whichpriority is claimed under 35 U.S.C. §120; and this application claimspriority of Application No. 11-263264 filed in Japan on Sep. 17, 1999under 35 U.S.C. §119.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for producing reduced ironwhich comprises (mixing a reducing agent and iron oxide, agglomeratingthe mixture, drying the compacts (pellets or briquettes) in a dryer, andreducing the dried compacts in a high temperature atmosphere in areducing furnace. This invention also relates to a method for dryingcompacts, which method is applied to the apparatus.

2. Description of the Related Art

To produce reduced iron, the first step is to mix an iron ore powder, acoal powder, a limestone powder, and a binder, and to compress andagglomerate the mixture to form wet compacts called green compacts.Then, the wet compacts are dried to some degree to form dry compacts.The dry compacts are heated to a high temperature in a reducing furnace,where the iron oxide in the iron ore is reduced with the coal (areducing agent) to form reduced iron compacts.

An example of a conventional apparatus for producing reduced iron isexplained by way of FIG. 6. At an upper portion of a circular rotaryhearth type of reducing furnace 1, there are provided a device 2 forintroducing compacts (dry compacts), and an off-gas duct 3 ordischarging a hot off-gas, a residual form of a gas used in reduction.Inside the furnace 1, a discharger 4 is provided for discharging reducedcompacts P (reduced iron compacts). On a circumferential sidewall of thefurnace 1, a plurality of burners 5 is provided for generating areducing hot gas.

Powders of coal (a reducing agent), iron ore, etc. as raw materials aremixed with a binder, and the mixture is fed to a pelletizer or abriquetter 6, where compacts (wet compacts) are formed. The resultingcompacts are sent to a dryer 7, where the compacts are dried at about120 to 150° C. to become dry compacts the dry compacts are supplied tothe rotary hearth of the reducing furnace 1 via the introducing device2.

In the reducing furnace 1, fuel and combustion air are fed to theburners 5, which generate a high temperature hot gas. The hot gas turnsin the direction of a dashed arrow, and during this motion, exerts areductive action on the compacts, an object to be treated, in a hightemperature atmosphere. A hot off-gas discharged through the off-gasduct 3 is primarily cooled by a primary cooler 8 of a water spray type,and then brought to a heat exchanger 9, where the off-gas exchanges heatwith the combustion air. Further, the off-gas is secondarily cooled by asecondary cooler 10 of a water spray type to about 300° C., for example.Then, the cooled off-gas is conveyed to the dryer 7 to dry the compacts.Then, the off-gas is passed through a dust collector 11, where it iscleaned, and then dissipated into the air.

When the rotary hearth inside the reducing furnace 1 makes nearly onerotation in the direction of a solid arrow in FIG. 6, the reducedcompacts P are discharged from the screw type discharger 4. The compactsare delivered to a portable container 13 by a discharge chute 12, andthen transported to a subsequent step.

In the dryer 7 of the foregoing conventional apparatus for producingreduced iron, the hot off-gas discharged from the reducing furnace 1 andcooled by the water spray type of primary cooler 8 and secondary cooler10 is used as a heat source for drying the compacts (wet compacts) at atemperature of about 120 to 150° C. That is, the compacts are dried withthe hot off-gas which is very rich with steam. Hence, during theunstable state which occurs immediately after initiation of operation ofthe apparatus, moisture is condensed onto the surfaces of the wetcompacts. As a result, sticking of the wet compacts to each otheroccurs, whereupon the wet compacts may lump together, becoming largemasses. In a situation such as that immediately after the start ofoperation, the properties, such as temperature and flow rate, of the hotoff-gas discharged from the reducing furnace 1 are not stable, so thatdrying in the dryer 7 is unstable. This may cause the problem of wetcompact lumping.

The wet compacts, which have been treated in the dryer 7 during such anunsteady operation, may have moisture remaining in the compacts. If suchwet compacts are rapidly heated in the reducing furnace 1 in asubsequent step, surface portions of the compacts may peel off, or thecompacts may rupture.

The heating gas in a dryer like the above-mentioned dryer 7, or in adryer using hot air from a heat exchanger or the like as a heat sourcefor drying compacts (wet compacts), may cause compact rupture, or theformation of a combustible gas from coal in the compacts, if thetemperature of the heating gas is too high. To avoid these risks, themaximum temperature of the heating gas is set at 200° C. or lower.Depending in the moisture content, etc. of the heating gas, however, ahigher gas temperature than that may be set. Since a conventional dryeruses a heating gas whose temperature has been set to be somewhat low, ithas posed the problem of taking considerable time for drying compacts.

In an apparatus for producing reduced iron, which uses coal as areducing agent, volatile matter (hereinafter referred to as VM), such asCO, CH₄, H₂O, CO₂, and N₂, occurs from coal, if the temperature of thheating gas is too high. At a high oxygen concentration, therefore, thecoal may catch fire. Once VM develops in the dryer, the VM cannot beutilized as a heat source in the reducing furnace in the subsequentstep. This poses the disadvantage that the thermal efficiency of thereducing furnace is lowered. If the temperature of the heating gas isthe sulfuric acid dew point (120° C.) or lower, on the other hand,corrosion will be induced because of dew formation in piping, etc.inside the dryer.

As described above, temperature control for the heating gas is of vitalimportance in efficiently drying compacts (wet compacts) in a dryer.There has been an intense demand for the realization of a dryer capableof producing stable drying conditions.

SUMMARY OF THE INVENTION

The present invention has been proposed in light of these circumstances.It is an object of this invention to provide an apparatus for producingreduced iron, which can perform highly efficient, stable drying in adryer and produce high quality reduced iron stably; and also to providea method for drying compacts which is applied to the apparatus.

A first aspect of the present invention, as a means of attaining theabove object, is a method for drying compacts, the method being appliedto an apparatus for producing reduced iron by mixing and agglomerating apowder of a reducing agent and a powder of iron oxide in a pelletizer toform compacts or in a briquetter to form briquettes, drying the compacts(pellets or briquettes) in a dryer, and reducing the dried compacts in ahigh temperature atmosphere in a reducing furnace, wherein

a temperature range of a heating gas supplied to the dryer is set basedon the following equation:

Sulferic acid dew point <T_(g) <100/40·C_(H2O)+200

where T_(g) denotes the temperature (° C.) of the heating gas, andCH_(H2O) denotes a moisture concentration (vol %) in the heating gas.

a temperature range of a heating gas supplied to the dryer is set basedon the following equation:

Sulfuric acid dew point≦T_(g)≦100/40·C_(H2O)+200

where T_(g) denotes the temperature [° C.] of the heating gas, andC_(H2O)denotes a moisture concentration [vol %] in the heating gas.

According to the above aspect of the invention, a high gas temperatureadapted for the moisture concentration (moisture content) in the heatinggas can be set. Thus, the drying can be shortened, and highly efficient,stable drying can be performed, so that high quality reduced iron can beproduced stably. Furthermore, the temperature of the heating gas on theexit side of the dryer is at a high temperature which is above thesulfuric acid dew point. Thus, acid corrosion of piping, etc. minimallyoccurs.

In the method for drying compacts as the first aspect of the invention,the apparatus for producing reduced iron may use coal as the reducingagent, and the temperature T_(g) of the heating gas may be set atT_(g)≦300° C. Thus, compact rupture or formation of VM from coal in thedryer can be prevented. Consequently, ignition of coal, or a decrease inthe thermal efficiency in the reducing furnace in the subsequent stepcan be prevented.

A second aspect of the invention is an apparatus for producing reducediron, comprising a pelletizer or a briquetter for mixing andagglomerating a reducing agent and iron oxide to form compacts, a dryerfor drying the compacts, a reducing furnace for reducing the driedcompacts in a high temperature atmosphere, a first heat exchanger forperforming heat exchange between a hot off-gas discharged from thereducing furnace and combustion air to be supplied to the reducingfurnace, and a cooler for cooling the hot off-gas, wherein

a second heat exchanger for heating drying air is disposed on the exitside of the first heat exchanger, and the drying air heated by thesecond heat exchanger is supplied to the dryer.

According to this aspect of the invention, compacts (wet compacts) aredried with moisture-poor drying air. Thus, sticking of the compacts toeach other does not take place (compacts are prevented from becominglarge lumps), and the compacts are uniformly

In the apparatus for producing reduced iron as the second aspect of theinvention, the cooler, dried. Since the compacts are uniformly dried toleave no moisture behind inside the compacts, peeling of the surfaceportion, or rupture of the compacts can be avoided in the reducingfurnace in the subsequent step. Moreover, high quality dry compacts areformed, and the supply of these compacts to the rotary hearth typereducing furnace can result in the stable production of high qualityreduced iron.

In the apparatus for producing reduced iron as the second aspect of theinvention, the cooler may be a water spray type of first cooler which isprovided upstream from the first heat exchanger, an air introductiontype of second cooler may be provided on a path bypassing the firstcooler, and a control means may be provided for switching a valveprovided at a bifurcation upstream from the bypass path to select eitherthe first cooler or the second cooler based on a trade-off between theflow rate of the hot off-gas and the flow rate of the compacts to thedryer. Thus, in addition to the same actions and effects as obtained bythe second aspect of the invention, the heat exchange efficiency of thefirst heat exchanger and the second heat exchanger is increased.Consequently, even more efficient, stable drying can be performed in thedryer.

In the apparatus for producing reduced iron as the second aspect of theinvention, moreover, a hot stove for generating a hot gas may bedisposed on a drying air introduction side of the dryer, and the hot gasgenerated by the hot stove and the drying air heated by the second heatexchanger may be supplied to the dryer. Thus, in addition to the sameactions and effects as are obtained by the second aspect of theinvention, there is obtained the advantage that the temperature and flowrate of the drying air fed to the dryer can be adjusted more easily.

A third aspect of the present invention is an apparatus for producingreduced iron by agglomerating a powder of a reducing agent and a powderof iron oxide in a pelletizer to form compacts or in a briquetter toform briquettes, drying the compacts in a dryer, and reducing the driedcompacts in a high temperature atmosphere in a reducing furnace, whereina hot stove for generating a hot gas is disposed on a drying gasintroduction side of the dryer, and the hot gas from the hot stove issupplied to the dryer as a drying gas.

According to this aspect of the invention, in addition to the sameactions and effects as obtained by the second aspect of the invention,there is obtained the advantage that the operation of the dryer can becontrolled easily by arbitrarily adjusting the temperature and flow rateof the hot gas generated by the hot stove.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description takenin connection with the accompanying drawings, in which:

FIG. 1 (a) shows data indicating the conditions for and the results ofcompact (wet green compact, WGC) drying as a first embodiment of thepresent invention;

FIG. 1 (b) is a graph showing the relation between the moistureconcentration in a heating gas and the temperature of the heating gas;

FIG. 2 is a schematic constitution drawing of an apparatus for producingreduced iron, showing a second embodiment of the invention;

FIG. 3 is a schematic constitution drawing of an apparatus for producingreduced iron, showing a third embodiment of the invention;

FIG. 4 is a schematic constitution drawing of an apparatus for producingreduced iron, showing a fourth embodiment of the invention;

FIG. 5 is a schematic constitution drawing of an apparatus for producingreduced iron, showing a fifth embodiment of the invention; and

FIG. 6 is a schematic constitution drawing of a conventional apparatusfor producing reduced iron.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings, which in no way limit theinvention.

[First Embodiment]

FIG. 1(a) shows data indicating the conditions for and the results ofcompact (wet green compact, WGC) drying as a first embodiment of thepresent invention. FIG. 1(b) is a graph showing the relationship betweenthe moisture concentration in a heating gas and the temperature of theheating gas.

As shown in FIGS. 1(a) and 1(b), the inventors conducted experimentswith an apparatus for producing reduced iron by agglomerating a powderof a reducing agent and a powder of iron oxide in a pelletizer to formcompacts or in a briquetter to form briquettes, drying the compacts in adryer, and reducing the dried compacts in a high temperature atmospherein a reducing furnace. From the experiments, they found a method forsetting the temperature range of a heating gas for drying the compactsin the dryer as an equation dependent on the moisture concentration. Theequation is offered below. In the column “VM generation” of FIG. 1(a),◯represents no generation of VM, and X represents the generation of VM.In the column “Compact rupture”,◯ represents no compact rupture, and Xrepresents compact rupture. In the column “Evaluation”, represents◯ forboth of VM generation and compact rupture, while X represents X for oneor both of VM generation and compact rupture. In FIGS. 1(a) and 1(b),the bulk flow velocity of the heating gas is 5.0 m/s or less.

Sulfuric acid dew point <T_(g) <100/40·C_(H20)+200 where T_(g) denotesthe temperature (° C.) of the heating gas, and C_(H20)denotes themoisture concentration (vol %) in the heating gas.

According to the above equation, a high gas temperature adapted for themoisture concentration (moisture content) in the heating gas can be set.Thus, the drying time can be shortened, and highly efficient, stabledrying can be performed, so that high quality reduced iron can beproduced stably. Furthermore, the temperature of the heating gas on theexit side of the dryer is at a high temperature which is above thesulfuric acid dew point. Thus, acid corrosion of piping, etc. minimallyoccurs.

In the apparatus for producing reduced iron, which uses coal containingVM as the reducing agent, the temperature T_(g) of the heating gas isset at T_(g) ≦300° C. Thus, compact rupture or evaporation of VM fromcoal in the dryer can be prevented. Consequently, ignition of the coal,or a decrease in the thermal efficiency in the reducing furnace in thesubsequent step can be prevented.

As described above, a high gas temperature adapted for the moistureconcentration (moisture content) in the heating gas can be set accordingto the present embodiment. Therefore, wet compacts can be prevented frombecoming large lumps, and peeling of the surface portion of thecompacts, or rupture of the compacts in the reducing furnace can beavoided, in an iron oxide reducing apparatus, as shown in FIG. 6, whichcools a hot off-gas from the reducing furnace by a water spray typeprimary cooler and a water spray type secondary cooler, and which has adryer using the cooled hot off-gas as a heating gas. Needless to say,the present embodiment can be applied to an iron oxide reducingapparatus equipped with a dryer using hot air from a heat exchanger orthe like as a heat source for drying compacts (wet compacts).

[Second Embodiment]

FIG. 2 is a schematic constitution drawing of an apparatus for producingreduced iron, showing a second embodiment of the invention. In FIG. 2,the same members as in FIG. 6 explained in connection with the earliertechnology are assigned the same reference numerals, and overlappingexplanations are omitted.

In the present embodiment, a heat exchanger 20 for heating incoming airis provided. Drying air, which has been heated by the heat exchanger 20,is supplied to a dryer 7. This moisturepoor drying air dries thecompacts (wet compacts).

As shown in FIG. 2, the heat exchanger 20 of the invention (the secondheat exchanger in the second aspect of the invention) is disposed on theexit side of a heat exchanger 9 (the first heat exchanger in the secondaspect of the invention). This heat exchanger 20 heats incoming air, forexample, by passing a constant amount of the incoming air through apipe, and flowing a hot off-gas from the heat exchanger 9 outside thepipe for heat exchange. This heated incoming air is supplied to thedryer 7 as drying air.

On the exit side of the heat exchanger 20, a secondary cooler 10 of awater spray type is disposed for cooling the hot off-gas discharged fromthe heat exchanger 20. On the exit side of the secondary cooler 10, adust collector 11 is disposed for cleaning the cooled hot off-gas. Otherconstitutions are the same as in FIG. 6 showing the earlier technology,and their explanations are omitted.

According to the foregoing constitution, a powder of coal (reducingagent) and a powder of iron ore (iron oxide) as raw materials are formedinto compacts by a pelletizer or a briquetter 6, and dried by the dryer7. Then, the dried compacts (dry compacts) are fed to an introducingdevice 2 of a reducing furnace 1.

The drying air fed to the dryer 7 is the incoming air heated by the heatexchanger 20. This incoming air flows as an up flow through an inlet ata lower portion of the dryer 7, and dries the compacts (wet compacts).Then, this drying air flows as a downflow, is discharged out of thesystem through an outlet, and dissipated into the air. Inside the dryer7, the compacts (wet compacts) are dried with the drying air which isscant in moisture. Thus, the condensation and deposition of moisture onthe compacts are prevented. Consequently, sticking of the compacts toeach other does not take place, and the compacts are uniformly dried.

While a rotary hearth of the reducing furnace 1 is making nearly onerotation, the dried compacts (dry compacts) fed onto the rotary hearthundergo a reductive action by radiant heat due to combustion caused by aburner 5 supplied with fuel and combustion air. The reduced compacts Pare discharged from a screw type discharger 4, delivered to a portablecontainer 13 by a discharge chute 12, and transported to a subsequentstep.

The hot off-gas is discharged from an off-gas duct 3, and primarilycooled by a primary cooler 8 of a water spray type, and then brought tothe heat exchanger 9, where the off-gas exchanges heat with thecombustion air. Further, the off-gas is carried to the heat exchanger 20for heat exchange with incoming air, and secondarily cooled by thesecondary cooler 10 of a water spray type. Then, the cooled off-gas ispassed through the dust collector 11, where it is cleaned, and thendissipated into the air. According to the present embodiment, asdescribed above, the heat exchanger 20 for heating incoming air isprovided on the exit side of the heat exchanger 9. The heated incomingair is supplied to the dryer 7 as drying air. Thus, the compacts (wetcompacts) are dried with the drying air which is scant in moisture. As aresult, sticking of the compacts to each other does not take place(growth of the compacts to large lumps is prevented), and the compactsare uniformly dried. Since the compacts are uniformly dried to leave nomoisture behind inside the compacts, peeling of the surface portion, orrupture of the compacts can be avoided, in the reducing furnace 1 in thesubsequent step. Moreover, high quality dry compacts are formned, andthe supply of these compacts to the rotary hearth type reducing furnacecan result in the stable production of high quality reduced iron.

In the present embodiment as well, the temperature of the heating gas(incoming air) in the dryer 7 may be controlled in accordance with themoisture concentration (moisture content) of the heating gas by use ofthe equation indicated in the First Embodiment, thereby achieving afurther improvement in the drying efficiency.

[Third Embodiment]

FIG. 3 is a schematic constitution drawing of an apparatus for producingreduced iron, showing a third embodiment of the invention. In FIG. 3,the same members as in FIG. 6 explained in connection with the earliertechnology, and in FIG. 2 of the Second Embodiment are assigned the samereference numerals, and overlapping explanations are omitted.

In the present embodiment, a bypass path 21 is provided for bypassingthe primary cooler 8 in the Second Embodiment (the first cooler in theaforementioned optional aspect of the invention), an air introductiontype cooler (the second cooler in the aforementioned optional aspect ofthe invention) 22 is provided on the bypass path 21, and a controller (acontroller means) 24 is provided for switching a valve 23 provided at abifurcation upstream from the bypass path 21 to select either theprimary cooler 8 or the cooler 22 based on a trade-off between the flowrate of the hot off-gas and the flow rate of the compacts to a dryer 7.In more detail, the controller 24 receives a detection signal from aflow meter 25 which is interposed downstream from an off-gas duct 3 todetect the flow rate of the hot off-gas, and a detection signal from aflow meter (not shown) which is provided in the dryer 7 to detect theflow rate of compacts (wet compacts) being fed to the dryer 7.

According to the present embodiment, in addition to the same actions andeffects as obtained by the Second Embodiment, the heat exchangeefficiency of a heat exchanger 9 and a heat exchanger 20 is increased,for example, by passing the hot off-gas through the air introductiontype cooler 22, rather than passing the hot off-gas through the primarycooler 8, during the unstable condition which occurs immediately afterinitiation of operation of the apparatus. Consequently, even moveefficient, stable drying can be performed in the dryer 7. On thisoccasion, condensation of moisture on the wet compacts, followed bymutual sticking of the compacts and associated growth of the compactsinto large lumps, can be prevented. Furthermore, peeling of the surfaceportion from the compacts, or rupture of the compacts can be avoided inthe reducing furnace 1 in the subsequent step.

In the present embodiment as well, the temperature of the heating gas(incoming air) in the dryer 7 may be controlled in accordance with themoisture concentration (moisture content) in the heating gas by use ofthe equation indicated in the First Embodiment, whereby a furtherimprovement in the drying efficiency can be achieved.

As a modification of the present embodiment, the primary cooler 8 may becomposed of a cooler having a water line and an air line, instead ofproviding the bypass path 21. Either the water line or the air line maybe selected by the controller 24 based on a trade-off between the flowrate of the hot off-gas and the flow rate of compacts to the dryer.

[Fourth Embodiment]

FIG. 4 is a schematic constitution drawing of an apparatus for producingreduced iron, showing a fourth embodiment of the invention. In FIG. 4,the same members as in FIG. 6 explained in connection with the earliertechnology, and in FIG. 2 of the Second Embodiment are assigned the samereference numerals, and overlapping explanations are omitted.

The present embodiment corresponds to the Second Embodiment of FIG. 2,in which a hot stove 30 is additionally disposed on a drying airintroduction side of a dryer 7, and is connected to a drying air inletlocated at a lower portion of the dryer 7 so that a hot gas generated bythe hot stove 30 is supplied through the inlet together with dryingincoming air from a heat exchanger 20. Other constitutions are the sameas in the Second Embodiment.

The drying air fed to the dryer 7 is a combination of the incoming airheated by the heat exchanger 20, and the hot gas generated by the hotstove 30 and supplied supplementally. This combined fluid flows as an upflow through the drying air inlet at the lower portion of the dryer 7,and dries the compacts (wet compacts). Then, this fluid flows as adownflow, is discharged out of the system through an outlet, anddissipated into the air. Inside the dryer 7, the wet compacts are driedwith the drying air which is scant in moisture. Thus, the condensationof moisture on the wet compacts is prevented. Consequently, sticking ofthe wet compacts to each other does not take place, and the wet compactsare uniformly dried.

In response to changes in the temperature and flow rate of the dryingair fed from the heat exchanger 20, the temperature and flow rate of thehot gas fed from the hot stove 30 are adjusted, whereby the operation ofthe dryer 7 can be controlled easily. A drying gas fed to the dryer 7 isthe hot gas generated by the hot stove 30. the hot gas generated by thehot stove 30 flows as an up flow through the drying gas inlet at thelower portion of the dryer 7, and dries wet compacts. Then, the hot gasflows as a downflow, is discharged out of the system through an outlet,and dissipated into the air. Inside the dryer 7, the wet compacts aredried with the drying gas which is scant in moisture. Thus, thecondensation of moisture on the wet compacts is prevented. Consequently,sticking of the wet compacts to each other does not take place, and thewet compacts are uniformly dried.

[Fifth Embodiment]

FIG. 5 is a schematic constitution drawing of an apparatus for producingreduced iron, showing a fifth embodiment of the invention. In FIG. 5,the same members as in FIG. 6 explained in connection with the earliertechnology, and in FIG. 2 of the Second Embodiment are assigned the samereference numerals, and overlapping explanations are omitted.

The present embodiment corresponds to the Second Embodiment of FIG. 2,in which the heat exchanger 20 is abolished, and only a hot stove 30 isdisposed on a drying gas introduction side of a dryer 7, and isconnected to a drying gas inlet located at a lower portion of the dryer7 so that a hot gas generated by the hot stove 30 is supplied throughthe inlet. Other constitutions are the same as in the Second Embodiment.

A drying gas fed to the dryer 7 is the hot gas generated by the hotstove 30. The hot gas generated by the hot stove 30 flows as an upflowthrough the drying gas inlet at the lower portion of the dryer 7, anddries wet compacts. Then, the hot gas flows as a downflow, is dischargedout of the system through an outlet, and dissipated into the air. Insidethe dryer 7, the wet compacts are dried with the drying gas scant inmoisture. Thus, the condensation of moisture on the wet compacts isprevented. Consequently, sticking of the wet compacts to each other doesnot take place, and the wet compacts are uniformly dried.

The foregoing constitution eliminates influences from the temperatureand flow rate of the hot off-gas from the reducing furnace 1. Theoperation of the dryer 7 can be controlled easily by arbitrarilyadjusting the temperature and flow rate of the hot gas generated by thehot stove 30.

According to the present embodiment, as described above, the hot stove30 for generating a hot gas is disposed, and the hot gas is supplied tothe dryer 7 as a drying gas. Thus, in addition to the same actions andeffects as obtained by the Second Embodiment, there is obtained theadvantage that the temperature and flow rate of the drying gas fed tothe dryer 7 can be adjusted more easily.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. An apparatus for producing reduced iron,comprising a pelletizer or a briquetter for mixing and agglomerating areducing agent and iron oxide to form compacts, a dryer for drying thecompacts, a reducing furnace for reducing the dried compacts in a hightemperature atmosphere, a first heat exchanger for performing heatexchange between a hot off-gas discharged from the reducing furnace andcombustion air to be supplied to the reducing furnace, and a cooler forcooling the hot off-gas, wherein a second heat exchanger for heatingdrying air is disposed on an exit side of the first heat exchanger, andthe drying air heated by the second heat exchanger is supplied to thedryer.
 2. The apparatus for producing reduced iron as claimed in claim1, wherein the cooler is a water spray type first cooler providedupstream from the first heat exchanger, an air introduction type secondcooler is provided on a path bypassing the first cooler, and a controlmeans is provided for switching a valve provided at a bifurcationupstream from the bypass path to select either the first cooler or thesecond cooler based on a trade-off between a flow rate of the hotoff-gas and a flow rate of the compacts to the dryer.
 3. The apparatusfor producing reduced iron as claimed in claim 1, wherein a hot stovefor generating a hot gas is disposed on a drying air introduction sideof the dryer, and the hot gas generated by the hot stove and the dryingair heated by the second heat exchanger are supplied to the dryer.
 4. Anapparatus for producing reduced iron by agglomerating a powder of areducing agent and a powder of iron oxide in a pelletizer to formcompacts or in a briquetter to form briquettes, drying the compacts in adryer, and reducing the dried compacts in a high temperature atmospherein a reducing furnace, wherein a hot stove for generating a hot gas isdisposed on a drying gas introduction side of the dryer, and the hot gasfrom the hot stove is supplied to the dryer as a drying gas at atemperature according to the following formula: Sulfuric acid dew point≦T_(g)≦100/40·C_(H2O)+200 where T_(g) denotes the temperature [C°] ofthe heating gas, and C_(H2O) denotes the moisture concentration [vol %]in the heating gas.